JP4507784B2 - Vacuum forming method for thermoplastic resin foam sheet - Google Patents

Description

  The present invention relates to a vacuum forming method for a thermoplastic resin foam sheet.

Thermoplastic resin foam molded articles are excellent in light weight, recyclability, heat insulation, and the like, and are therefore used in various applications such as automotive parts materials, building materials, and packaging materials.
When a thermoplastic resin foam molded article is used as described above, after producing a thermoplastic resin foam sheet, the thermoplastic resin foam sheet is shaped into a desired shape by a secondary molding method such as vacuum molding. It is often used as a thermoplastic resin foam molded article. As a method of vacuum forming a thermoplastic resin foam sheet, a thermoplastic resin foam sheet is supplied between a pair of male and female molds having a predetermined gap when the molds are clamped, and both molds are kept clamped. A method is known in which a vacuum pressure is reduced from the surface to shape a foamed sheet into a void shape to obtain a thermoplastic resin foamed molded article (see, for example, Patent Document 1).

JP 54-148863 A

As the foam sheet, a sheet having a high foaming ratio and a large thickness is desired. According to the said method, compared with the raw fabric foam sheet used for vacuum forming, a foam ratio is high and a thick sheet can be obtained. However, in the above method, since the raw foam sheet can be expanded only by the gap formed when the pair of molds are clamped, the thickness of the obtained thermoplastic resin foam sheet is about twice the thickness of the raw sheet. However, the expansion ratio was still not satisfactory.
In order to obtain a thermoplastic resin foam sheet having a sufficiently high foaming ratio and a thicker thickness than the original foam foam sheet by the above method, it is necessary to use a mold having a large void portion. Even if this is done, the voids may not be filled with the original fabric foamed sheet, and it is still difficult to obtain a thermoplastic resin foamed sheet having a higher foaming ratio than that of the original fabric foamed sheet.
The present invention provides a method for producing a thermoplastic resin foam sheet having a high expansion ratio and a large thickness.

That is, the present invention uses a molding die A that can be vacuum-sucked from the molding surface of the molding die and a molding die B having a sheet fixing member at least on the outer edge of the molding surface, and includes a vacuum for a thermoplastic resin foam sheet including the following steps: This is a molding method.
(1) Step of heating and softening the thermoplastic resin foam sheet (2) Step of supplying the thermoplastic resin foam sheet obtained in step (1) between the mold A and the mold B (3) Heat softening While sandwiching the thermoplastic resin foam sheet between the molds, close both molds until the clearance between the molds at the outer edge of the mold surface is equal to or less than the thickness of the sheet, Step (4) of contacting the surface of the foamed sheet (4) Step of starting vacuum suction from the molding surface of the mold A (5) after the entire molding surface of the mold B and the surface of the foamed sheet B are contacted in the step (3). ) A step of opening and shaping the mold until the sheet between the molding surfaces reaches a desired thickness of the molded product while continuing the vacuum suction (6) A step of stopping the vacuum suction and opening the molding die and taking out the molded product

  According to the method for producing a thermoplastic resin foam sheet of the present invention, it is possible to produce a thermoplastic resin foam sheet having a high foaming ratio and a large thickness.

  Hereinafter, an example of the present invention will be described in detail with reference to FIG. 1, but the present invention is not limited to this example.

  As shown in FIG. 1, the present invention uses a molding die A (4) that can be vacuum-sucked from the molding surface of the molding die and a molding die B (5) having a sheet fixing member (6) at least on the outer edge of the molding surface. Then, the thermoplastic resin foam sheet (1) in a state of being fixed by the clip member (2) and heated and softened by the infrared heater (3) is formed. The mold B may be vacuum suckable from the molding surface. Examples of the mold to be used include a male mold on one side, a female mold on the other side, a mold between female dies, a pair of plate-shaped molds, and the like. What is necessary is just a type in which the entire molding surface of the molding die B and the foam sheet surface come into contact when both molding dies are closed until the clearance becomes equal to or less than the thickness of the foam sheet.

  Examples of the mold that can be vacuum-sucked from the molding surface of the molding die include a mold in which at least a part of the molding surface is made of a sintered alloy and a mold in which holes are provided in at least a part of the molding surface. The The number, position, and hole diameter of the holes provided in the mold are not particularly limited. By vacuum suction through the holes, the thermoplastic resin foam sheet supplied between the molds is shaped into a mold surface. Anything that can be shaped is acceptable.

The material of the mold is not particularly limited, but is usually made of metal from the viewpoints of dimensional stability, durability, thermal conductivity, and the like, and is preferably made of aluminum from the viewpoints of cost and lightness.
Moreover, it is preferable that a shaping | molding die is a structure which can adjust temperature with a heater, a heat medium, etc. From the viewpoint of enhancing the slipperiness with the foam sheet and from the viewpoint of preventing the foam sheet from being cooled before the completion of molding, the molding surface of the molding die is preferably set to 30 to 80 ° C, and 50 to 60 ° C. More preferably.

As one or both of the molds, it is preferable to use a mold having an airtight holding portion. When such a mold is used, it is easy to maintain the degree of vacuum in the cavity when vacuum suction is performed, and a molded product with extremely small sink marks can be obtained.
Examples of the mold having the hermeticity holding portion include a mold in which the outer edge portion of the molding surface of at least one of the molds is movable in the opposing mold direction. In the case of such a mold, it is preferable that the movable part can be stored in the mold so that the movable part is on the same plane as the outer edge of the molding surface when the mold is closed. In such a mold, the movable part protrudes as the mold is opened, so that the degree of vacuum in the cavity is easily maintained in the mold opening process described later.

As another example of the mold having the airtight holding portion, a mold having a cushioning material at the outer edge of the molding surface of at least one of the molds can be cited. Usually, the foam sheet has minute irregularities on the surface. In the case of a mold having a cushioning material, the cushioning material comes into close contact with the surface of the foamed sheet having minute irregularities when the mold is closed, so that it is easy to maintain the degree of vacuum in the cavity when vacuum suction is performed. Examples of the buffer material include rubber and foam.
It is also possible to use a pair of molds configured such that when the mold is closed, the other mold is covered by an airtight holding portion provided on the outer periphery of one mold.

  As shown in FIG. 1- (2), the molding die B has a sheet fixing member (6) at least on the outer edge of the molding surface. The sheet fixing member may be provided on at least a part of the molding surface. In the step (5) of the vacuum forming method of the present invention described later, the sheet fixing member is fixed so that the foamed sheet is fixed to the mold B when the mold is opened while performing vacuum suction from the molding surface of the mold A. For example, an adhesive material may be provided on the outer edge of the molding surface, or a pin, hook, clip, slit, or the like may be provided. By using such a mold, it becomes easy to shape the foamed sheet into a molded surface. The mold A may also have a sheet fixing member at least on the outer edge of the molding surface.

  As the mold, it is preferable to use a mold in which the height of the cavity formed when the mold is closed is about 0.8 to 2 times the thickness of the foamed sheet obtained in the step (1). The height of the cavity is the distance between the molding surfaces corresponding to the thickness direction of the foam sheet supplied between the molding dies. The cavity height does not need to be constant, and may be a cavity corresponding to the shape of a desired molded product. If the height of the cavity is too low, bubbles in the foam sheet may be crushed when the mold is closed. If it is too high, the mold surface of the mold and the surface of the foam sheet are brought into contact with each other even if vacuum suction is applied as described later. It becomes difficult to form, and even when brought into contact, bubbles are easily broken.

  FIG. 1- (1) shows the step (1) of heat-softening the thermoplastic resin foam sheet. In the step (1), the foam sheet is usually sandwiched between clamp frames, and the foam sheet is heated by a known heating device such as a far infrared heater, a near infrared heater, or a contact hot plate. It is preferable to use a far infrared heater because it can be efficiently heated in a short time. The heat treatment is preferably performed so that the surface temperature of the foamed sheet is near the melting point of the resin if the resin constituting the foamed sheet is a crystalline resin, and near the glass transition temperature if the resin is an amorphous resin. .

  FIG. 1- (2) shows the heat obtained in the step (1) between the molding die A that can be vacuum-sucked from the molding surface of the molding die and the molding die B having a sheet fixing member at least on the outer edge of the molding surface. The state which supplied the plastic resin foam sheet is shown.

  FIG. 1- (3) shows both molds until the heat-softened thermoplastic resin foam sheet is sandwiched between the molds and the clearance between both molds at the outer edge of the molding surface is equal to or less than the thickness of the sheet. Is closed, and the entire molding surface of the mold B is in contact with the foamed sheet surface. By closing both molds until the clearance between both molds at the outer edge of the molding surface is equal to or less than the thickness of the foam sheet, the foam sheet and the mold B are provided by the sheet fixing member provided at the outer edge of the molding surface of the mold B. The outer edge of the molding surface is fixed, and the entire molding surface of the molding die B comes into contact with the surface of the foamed sheet, so that the foaming sheet is shaped into the molding surface of the molding die B. In closing the mold, only one mold may be moved in the direction of the other mold, or both molds may be brought close to each other.

  1- (4) shows a state where vacuum suction is performed from the molding surface of the mold A. FIG. The vacuum suction starts after the entire molding surface of the mold B comes into contact with the foam sheet surface. Here, after the entire molding surface of the mold B and the foam sheet surface are in contact, the entire molding surface of the mold B and the foam sheet surface may be in contact with each other. When vacuum suction is performed after the entire molding surface of the mold B and the surface of the foam sheet are in contact with each other, usually from the time when the entire molding surface of the mold B and the surface of the foam sheet are in contact before the foam sheet is cooled. It is preferable to perform vacuum suction within 3 seconds.

  When a mold that can be vacuum-sucked from the molding surface is used as the mold B, the timing of starting vacuum suction from the mold B may be any time point from the step (1) to the step (4). Vacuum suction is started from the time when both molds are closed until the clearance between both molds in the normal step (3) becomes equal to or less than the thickness of the foam sheet. By vacuum suction from the mold B, the foamed sheet can be shaped into the molding surface of the mold B in a short time.

  The degree of vacuum suction is not particularly limited, but vacuum suction is preferably performed so that the degree of vacuum of the cavity is -0.05 to -0.1 MPa. The degree of vacuum is the pressure in the cavity with respect to atmospheric pressure. That is, “the degree of vacuum is −0.05 MPa” indicates that the pressure in the cavity is 0.95 MPa. The higher the degree of vacuum, the stronger the foam sheet is pressed against the mold, so that the foam sheet can be shaped according to the cavity shape. The vacuum degree of the cavity is a value measured at the cavity side opening of the hole to be vacuumed.

  FIG. 1- (5) shows a state where the mold is opened and shaped until the sheet between the molding surfaces reaches a desired thickness of the molded product. Open the mold while continuing vacuum suction. The mold opening speed and the degree of vacuum may be adjusted so that the foamed sheet is finally shaped into a desired molded product shape while maintaining the state where the foamed sheet is in contact with the molding surface of each mold.

  In the state where the mold is opened to a predetermined thickness, the foamed sheet is sufficiently cooled, then vacuum suction is stopped, the mold is opened, and the molded product is taken out. FIG. 1- (6) shows a state in which a mold (not shown) is opened to take out the molded product.

  In the present invention, a skin material may be placed in advance on the molding surface of one or both molds. As the skin material, the material and thickness are not particularly limited as long as the foamed sheet can be shaped into a molding surface by performing vacuum suction through the skin material. For example, a thermoplastic resin, thermosetting Resins, thermoplastic elastomers and other natural fibers, natural fibers such as rubber and hemp, minerals such as calcium silicate, etc. Examples of the form include films, sheets, nonwoven fabrics and woven fabrics. In addition, paper, synthetic paper made of propylene resin, styrene resin, or the like, a metal thin plate such as aluminum or iron, a metal foil, or the like can be used. The skin material may be a single layer or a multilayer, and may be a textured pattern such as embossed or printed or dyed.

It does not specifically limit as a thermoplastic resin foam sheet used by this invention, A well-known foam sheet can be used.
The resin constituting the thermoplastic resin foam sheet is an olefin homopolymer having 6 or less carbon atoms such as ethylene, propylene, butene, pentene, hexene, or two or more kinds selected from olefins having 2 to 10 carbon atoms. Olefin resins such as olefin copolymers obtained by copolymerizing monomers, ethylene-vinyl ester copolymers, ethylene- (meth) acrylic acid copolymers, ethylene- (meth) acrylic acid ester copolymers, ester-based resins Amide resin, styrene resin, acrylic resin, acrylonitrile resin, ionomer resin and the like. These resins may be used alone or as a blend of a plurality of resins. Among these resins, olefin resins are preferably used from the viewpoints of moldability, oil resistance, cost, and the like, and propylene resins are particularly preferably used from the viewpoint of rigidity and heat resistance of the obtained molded product.

  When using a foamed sheet made of a propylene resin, examples of the propylene resin constituting the foamed layer include a propylene homopolymer and a propylene copolymer containing 50 mol% or more of a monomer unit derived from propylene. The copolymer may be any of a block copolymer, a random copolymer, and a graft copolymer. As an example of the propylene-based copolymer that is preferably used, a copolymer of ethylene or an α-olefin having 4 to 10 carbon atoms and propylene can be given. Examples of the α-olefin having 4 to 10 carbon atoms include 1-butene, 4-methylpentene-1, 1-hexene, and 1-octene. The content of monomer units other than propylene in the propylene-based copolymer is preferably 15 mol% or less for ethylene and 30 mol% or less for α-olefins having 4 to 10 carbon atoms. One type of propylene resin may be used, or two or more types may be mixed and used.

Among the propylene resins, a long chain branched propylene resin or a high molecular weight propylene resin having a weight average molecular weight of 1 × 10 ⁵ or more is used in a finer particle by using 50% by weight or more of the thermoplastic resin constituting the foam layer. A propylene-based resin foam sheet having various bubbles can be obtained. Further, among such propylene resins, non-crosslinked propylene resins are preferably used because gels are unlikely to occur during sheet recycling.

Here, the long-chain branched propylene-based resin refers to a propylene-based resin having a degree of branching index [A] satisfying 0.20 ≦ [A] ≦ 0.98.
An example of a long-chain branched propylene-based resin satisfying the branching index [A] of 0.20 ≦ [A] ≦ 0.98 is propylene PF-814 manufactured by Basel.

The degree of branching index indicates the degree of long chain branching in a polymer, and is a numerical value defined in the following formula.
Branch index [A] = [η] _Br / [η] _Lin
Here, [η] _Br is the intrinsic viscosity of the propylene resin having a long chain branch, and [η] _Lin is a straight chain having the same monomer unit and the same weight average molecular weight as the propylene resin having the long chain branch. It is an intrinsic viscosity of a chain propylene resin.
Intrinsic viscosity, also called intrinsic viscosity, is a measure of the ability of a polymer to enhance solution viscosity. Intrinsic viscosity depends in particular on the molecular weight of the polymer molecules and the degree of branching. Therefore, by comparing the intrinsic viscosity of a polymer having long chain branches with the intrinsic viscosity of a linear polymer having the same weight average molecular weight as that of the polymer having long chain branches, the degree of branching of the polymer having long chain branches can be determined. It can be a scale. The method for measuring the intrinsic viscosity of a propylene-based resin is described by Elliott et al. [J. Appl. Polym. Sci. , 14, 2947-2963 (1970)], for example, a propylene resin is dissolved in tetralin or orthodichlorobenzene, and the intrinsic viscosity at 135 ° C. Can be measured.
The weight average molecular weight (Mw) of the propylene-based resin can be measured by various commonly used methods. L. The method disclosed by McConnel in American Laboratory, May, 63-75 (1978), that is, a low-angle laser light scattering intensity measurement method is particularly preferably used.
As an example of a method for polymerizing a high molecular weight propylene resin having a weight average molecular weight of 1 × 10 ⁵ or more, as described in JP-A No. 11-228629, a high molecular weight component is first polymerized, followed by low molecular weight. Examples thereof include a method of polymerizing components.

Among long-chain branched propylene resins or high-molecular-weight propylene resins, propylene resins having a uniaxial melt-extension viscosity ratio η ₅ / η _0.1 measured under the following conditions at around melting point + 30 ° C. are preferably 5 or more, more preferably 10 or more resins. The uniaxial melt extensional viscosity ratio is a value measured using an apparatus such as a uniaxial extensional viscosity measurement apparatus (for example, a uniaxial extensional viscosity measurement apparatus manufactured by Rheometrics, Inc.) at an elongation strain rate of 1 sec ⁻¹ . the uniaxial melt elongation viscosity after 0.1 seconds from the strain initiation and eta _0.1, the uniaxial melt elongation viscosity after 5 seconds and eta _5. By using a propylene-based resin having such uniaxial extensional viscosity characteristics, a foam sheet having finer bubbles can be produced.

  The foaming agent used to form the foamed sheet may be either a so-called chemical foaming agent or a physical foaming agent, or may be used in combination. Examples of the chemical foaming agent include a thermal decomposition type foaming agent that decomposes to generate nitrogen gas (azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, p-toluenesulfonylhydrazide, p, p'- Oxy-bis (benzenesulfonyl hydrazide) and the like, and pyrolytic inorganic foaming agents that decompose to generate carbon dioxide (sodium hydrogen carbonate, ammonium carbonate, ammonium bicarbonate, etc.) . Specific examples of the physical foaming agent include propane, butane, water, carbon dioxide gas, and the like. Among the above-exemplified foaming agents, water, carbon dioxide, and the like are used because the sheet is not easily deformed by secondary foaming during heating during vacuum forming, is a substance that is inert to high temperature conditions, and fire. Preferably used. The amount of the foaming agent used is appropriately selected according to the type of foaming agent and resin used so that a desired foaming ratio can be obtained. Usually, the foaming agent is used in an amount of 0.5 to 20 with respect to 100 weight of the thermoplastic resin. Parts by weight.

  Although the manufacturing method of the thermoplastic resin foam sheet used in the present invention is not particularly limited, a sheet obtained by extrusion molding using a flat die (T die) or a circular die is preferable, and a resin melted from a circular die is used. A method of extruding while foaming, stretching and cooling along a mandrel or the like is particularly preferably used. When the foamed sheet is produced by extrusion molding, the molten resin can be extruded from a die and solidified by cooling and then stretched. The foamed sheet may be a single layer or a multilayer, but from the viewpoint of preventing foam breakage during sheet production, a multilayered foam sheet having non-foamed layers in both outer layers is preferred. As the resin constituting the non-foamed layer, those described above as examples of the resin constituting the foamed layer can be used, but the same type of resin as that constituting the foamed layer is preferable. In the case of a propylene-based resin, the non-foamed layer is also preferably composed of a propylene-based resin.

The thermoplastic resin foam sheet used in the present invention may be a composite sheet obtained by laminating a single layer or multilayer foam sheet and another material. Such a composite sheet is obtained by laminating a foam sheet and another material by dry lamination, sand lamination, hot roll bonding, hot air bonding, or the like.
Examples of other materials to be laminated with the foamed sheet can be the same as the above-mentioned skin material. Especially when molding an automobile interior material by the molding method of the present invention, a sheet or nonwoven fabric made of a thermoplastic resin. Natural fibers such as woolen fabric and hemp are widely used, and when forming food containers, single-layer or multi-layer gas barrier films having a layer made of an ethylene-vinyl alcohol copolymer and CPP films are widely used. The

The multilayer thermoplastic resin foam sheet may be a multilayer foam sheet composed of a foam layer and a non-foam layer, or a multilayer foam sheet in which different foam layers are laminated. For example, as a multilayer foam sheet in which different foam layers are laminated, a foam layer _α having a foam ratio X _α of 2 to 20 times, a thickness T _{α of} 2 to 20 mm, and a basis weight R _α of 600 to 3000 g / m ² , and a foam ratio Multi-layer thermoplastic having foam layer _β where X _β is 4 to 40 times, thickness T _β is 2 to 12 mm, basis weight R _β is 100 to 600 g / m ² , and R _α / R _β = 2 to 30 A resin foam sheet can be used. When the above-mentioned multilayer thermoplastic resin foam sheet is vacuum-formed by the vacuum forming method of the present invention, the foam layer β expands more than the foam layer α, so that the molded product has excellent rigidity and buffering properties. Is obtained.

  The thermoplastic resin foam sheet used in the present invention may contain an additive. Examples of the additive include a filler (filler), an antioxidant, a light stabilizer, an ultraviolet absorber, a plasticizer, an antistatic agent, a colorant, a release agent, a fluidity-imparting agent, and a lubricant. Specific examples of the filler include inorganic fibers such as glass fibers and carbon fibers, inorganic particles such as talc, clay, silica, titanium oxide, calcium carbonate, and magnesium sulfate.

The molded product obtained by the vacuum forming method of the present invention has a large expansion ratio and thickness, is lightweight and has excellent heat insulation properties, and is used for packaging materials such as food containers, automobile interior parts, building materials, and home appliances. can do. Examples of automobile interior parts include door trims, ceilings, trunk sides, and the like. When the molded product obtained in the present invention is used as such a member, for example, when the temperature inside the vehicle is adjusted, The effect of being able to keep temperature for a long time is acquired. When used as a food container, it can be shaped and used in various shapes such as cups, trays, bowls, etc., and because it has excellent heat insulation properties, it can be used for filling soups heated to high temperatures or cooking in a microwave oven. It is preferably used for food containers.

Schematic of one aspect of the vacuum forming method of the thermoplastic resin foam sheet of the present invention

Explanation of symbols

1 Thermoplastic resin foam sheet 2 Clip member 3 Infrared heater 4 Vacuum mold A
5 Mold B having a sheet fixing member
6 Seat fixing member

Claims (1)

A method for vacuum forming a thermoplastic resin foam sheet, including the following steps, using a mold A that can be vacuum-sucked from a molding surface of the mold and a mold B having a sheet fixing member at least on the outer edge of the molding surface.
(1) Step of heating and softening the thermoplastic resin foam sheet (2) Step of supplying the thermoplastic resin foam sheet obtained in step (1) between the mold A and the mold B (3) Heat softening While sandwiching the thermoplastic resin foam sheet between the molds, close both molds until the clearance between the molds at the outer edge of the mold surface is equal to or less than the thickness of the sheet, Step (4) of contacting the surface of the foamed sheet (4) Step of starting vacuum suction from the molding surface of the mold A after the entire molding surface of the mold B and the surface of the foamed sheet are in contact in the step (3) (5) ) A step of opening and shaping the mold until the sheet between the molding surfaces reaches a desired thickness of the molded product while continuing the vacuum suction (6) A step of stopping the vacuum suction and opening the molding die and taking out the molded product

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